Minor

Someone under the age of consent, ie a child in the eyes of the Law. From a BDSM perspective sex with a minor is frowned upon since it is generally considered that they cannot give informed consent to this sort of activity.

(The age of majority in the UK is 18, however the age of consent for sex (both hetero and homosexual) is 16 for most acts, although some restictions apply. See age of consent for details.